This invention relates to flow rate sensors for use in relation to harvested crops, in particular a mass flow rate sensor adapted for operation in a crop harvester for grass-like crops such as sugar cane or corn silage. In one application, the mass flow rate sensor forms part of a yield monitoring system which can generate grop yield maps and similar data.
There exist flow rate sensors developed for the particular requirements of grain crops, including gamma ray absorption, impact plate, capacitive, pivoted auger with load cell and photo-detection techniques, as summarised by S. C. Borgelt and KA. Sudduth in Paper No. 921022 entitled xe2x80x9cGrain flow monitoring for in-field mappingxe2x80x9d, published by The American Society of Agricultural Engineers, 1992. However, these sensors are typically adapted to the particular requirements of grain flow, in particular varying moisture content, that affects the frictional characteristics and bulk density of harvested grain. Grain flow is much more homogeneous than the flow of sugar cane billets, which faces additional problems of crop contamination by dirt and extraneoous matter.
EP Patent Document No. 753720 (New Holland Belgium NV) describes a sensor which uses the change of momentum of moving grain flows over a curved plate as an indicator of flow rate. The plate is pivoted about a point chosen so that the momentum being measured in independent of the friction between the grain and the plate. Its correct operation depends on there being a continuous flow of material over the sensor.
U.S. Pat. No. 5,282,389 (Bassett et al.) describes an actuating arm projecting into a flow of grain being discharged from an elevator and uses the force of impact on a plate to measure mass flow. This sensor is particularly suited to grain harvesters when the flow of material is well controlled and confined.
German Patent Document No. 19524752 (Class KGAA) describes a system for calibrating measurement of material flow wherein material which has passed the flow sensor is selectively deflected into a measuring chamber for weighing. The system is arranged to automate the collection and weighing of a calibration sample while minimising the obstruction of material flow in an agricultural machine.
There have also been attempts to modify mass flow rate sensing techniques used in relation to forage crops, such as instrumenting the base unit drive shaft and blower shaft of a silage harvester with torque and speed sensors. R. Vansichen and J. de Baerdemaker found that silage flow rate was proportional to the measured power on each shaft, as set out in the article xe2x80x9cA measurement technique for yield mapping of corn silagexe2x80x9d, published in the Journal of Agricultural Engineering Research, Vol.55, 1993.
The present applicants investigated the instrumentation of the hydraulic drive systems for the chopper and the elevator in a cane harvester, as discussed by G. Cox, H. Harris and R. Pax and R. Dick in the paper xe2x80x9cMonitoring cane yield by measuring mass flow rate through the harvesterxe2x80x9d as published in the Proceedings of the 1996 Australian Society of Cane Technologies Conference1996. (A copy of this paper is annexed to the specification of Australian Provisional Patent Application, No. PP3089 dated Apr. 22, 1998.)
Australian Patent Application No. 35171/89 (Massey-Ferguson Australia) describes a crop flow monitoring technique whereby the torque requried to drive a threshing drum is employed for prompting the manual adjustment of harvester speed. Whilst PCT International Document No. WO 97/09592 describes an agricultural trailer for carrying portions of a crop as it is harvested, the trailer typically being towed alongside an operating harvester. The trailer also carries instrumentation for weighing the accumulating produce after harvesting and processing, which instrumentation is connected to GPS and data logging to provide yield maps. However, every trailer used for the harvest would require such a system which is uneconomical if applied to harvesting sugar cane. Furthermore the weighing system must operate over a large scale of accumulated weight thus introducing inaccuracies into the system.
The applicants have also conducted further development and testing of a yield monitoring system for sugar can using simplified mass flow rate sensors, for the chopper and elevator systems in a cane harvester, and a differential global positioning system (DGPS) technique. The results of this development are set out by G. Cox, H. Harris and R. Pax in the paper xe2x80x9cDevelopment and testing of a prototype yield mapping systemxe2x80x9d as presented to the ASSCT 1997 Conference held n Cairns, Australia. (A copy of this paper is also annexed to the abovementioned Australian provisional specification.)
The operating environment of a cane harvester is generally harsh, with a significant amount of mechanical noise, air flow and vibration which can have adverse effects on sensors used to determine mass flow rate. Further, cane harvesters operate in dirty or muddy environments and thus are often subject to periodic cleaning using high pressure liquid jets to dilodge dirt, mud and extraneous matter which tends to accumulate. The accumulation of dirt, mud and extraneous matter, along the subsequent cleaning, can have a deleterious effect on sensor components.
It is an object of the present invention to provide a mass flow rate sensor apparatus and method for use in harvesting grass-like crops which ameliorates or overcomes at least some of the problems associated with the prior art.
It is another object of the invention to provide a mass flow rate sensor apparatus and method which is adapted for use in billet harvesters for sugar cane.
It is another object of the invention to provide a mass flow rate sensor apparatus and method which may be conveniently integrated into a crop yield mapping system.
It is an yet another object of the invention to provide a crop yield mapping system.
Further objects will be evident from the following description.
In one aspect, although it need not be the only or indeed the broadest aspect, the invention resides in a mass flow rate sensor apparatus for a crop harvester having a floor section which is traversed by stalk portions of the harvest crop, said mass flow sensor apparatus including:
a) a weigh pad for receiving portions of the harvested crop;
b) first transducer means associated with the weigh pad for producing mass signals indicative of a mass received by the weigh pad; and
c) error correction means for correction of measurement errors in said mass signals;
d) whereby, in use, the weigh pad is mounted in the crop harvester at a location substantially co-planar with the floor section such that portions of the harvested crop traverse said weigh pad and the error correction means is operatively associated with said crop harvester.
Preferably the weigh pad includes a plate member that, in use, is movable with respect to the floor section.
In one form of weigh pad the plate member includes hinge means provided adjacent one end whereby, in use, the plate moves pivotally within an aperature in said floor section.
In another form of weigh pad the plate member includes guides or flexible supports whereby, in use, the plate member moves rectilinearly within an aperature in said floor section.
Suitably the first transducer means includes at least one load cell arranged to support the weigh pad.
In said one form of weigh pad, first transducer means includes at least one load cell disposed adjacent a second end of the plate member opposite said first end thereof.
In said other form of weigh pad, the first transducer means includes at least three load cells disposed under the plate member.
If required, the mass flow sensor apparatus further includes adjustable mounting means for said load cells enabling equalization of the output signals of respective load cells.
The error correction means may include an accelerometer for measuring vertical accelerations of the harvester to enable correction of mass measurements.
The error correction means may include an inclinometer for measuring the inclination of the weigh pad to enable correction of mass measurements.
Preferably the error correction means includes pre-processing means for periodically re-setting calibration of the tranducer means.
Suitably the pre-processing means is coupled to a proximity sensor that, in use, is arranged to cause said pre-processing means to re-set the calibration when there are no stalk portions on said weigh pad.
In a second aspect, the invention resides in a mass flow sensor apparatus for a billet type harvester for harvesting sugar cane, having an elevator with a plurality of flights that transfer batches of billets through an elevator housing and having a floor section proximate an upper end of the elevator, said mass flow sensor apparatus including:
a) a weigh pad for receiving batches of billets;
b) first transducer means operatively associated with the weigh pad for producing mass signals indicative of a mass received by the weigh pad; and
c) error correction means for correction of measurement errors in said mass signals;
d) whereby, in use, the weigh pad is substantially co-planar with the floor section in the elevator housing such that batches of billets traverse the weigh pad and the error correction means is operatively associated with the billet type harvester.
Preferably the weigh pad includes a plate member that, in use, is movable with respect to the floor section.
Suitably first transducer means includes at least one load cell arranged to support the weigh pad.
In preference the error correction means includes a pre-processing means for periodically re-zeroing calibration of the transducer means.
Preferably the pre-processing means is coupled to a proximity sensor that, in use, is arranged to cause said pre-processing means to re-zero the calibration when there are not billets on said weigh pad.
The proximity sensor may be of the inductive type and arranged to detect the passage of flights over the weigh pad.
The proximity sensor may be either of the optical type or of the capacitive type and arranged to detect an absence of billets on the weigh pad.
If required, the mass flow sensor apparatus may further include second transducer means operatively associated with elevator drive means for producing a speed signal indicative of the speed of the elevator drive means which drive said plurality of flights.
In a third aspect the invention may reside in a crop harvester, said harvester including a floor section which is traversed by stalk portions of a harvested crop and characterised by a mass flow sensor apparatus as set out above in relation to the first aspect of the invention.
Alternatively, the invention may reside in a billet type harvester for harvesting sugar cane, said harvester having an elevator with a plurality of flights that transfer batches of billets through an elevator housing with a floor section and an elevator drive means that drives said plurality of flights and characterised by a mass flow sensor apparatus as set out above in relation to the second aspect of the invention.
The billet type harvester may have an elevator with an extractor fan at an upper end thereof and include an air flow damper disposed between the weigh pad and the extractor fan.
Suitably the air flow damper includes a flexible curtain extending down from a ceiling of the elevator housing.
In a fourth aspect of the invention there is provided a method for sensing mass flow of a harvested crop in a crop harvester, which crop harvester has a floor section that is traversed by portions of a harvested crop, said method including the steps of:
a) weighing said portions of the harvested crop during traverse of the floor section to produce mass signals; and
b) correcting measurement errors in said mass signals, caused at least in part by crop harvester operations, to produce corrected mass measurements.
Preferably the step of weighing the portions of the harvested crop involves weighing said portions traversing a weigh pad that is provided in a substantially co-planar relation with the floor section of the harvester.
Suitably the step of correcting errors in mass signals further includes the step of periodically re-zeroing calibration applied to said mass signals when there are no harvested crop portions traversing the weigh pad.
In one form, the method further includes the step of calculating the mass flow rate using an average of a plurality of corrected mass signals obtained for each portion of said harvested crop.
In another form of the method, wherein the harvester is of the billet type having an elevator with a plurality of flights that transfer batches of billets through an elevator housing wherein said floor section is proximate an upper end of the elevator, further including the step of calculating the mass flow rate using one corrected mass signal obtained for each batch immediately prior to passage of a respective flight over the weigh pad.
In a fifth aspect of the invention there is provided a yield mapping system for a sugar cane crop, said system including:
i) a mass flow sensor apparatus as set out above in relation to the first or second aspects of the invention;
ii) a harvester ground speed sensor for providing, in use, ground speed signals indicative of the speed of the harvester;
iii) a differential global positioning system (DGPS) means for generating position signals indicative of harvester position within a field containing the crop;
iv) a pre-processor coupled to the mass flow sensor apparatus, the ground speed sensor and the DGPS means for recording the mass signals, ground speed signals and position signals against a common time base; and
v) processing means for producing a yield map from the recordings of said mass, ground speed and position signals.